726 JOUENAL OF THE EOYAL HORTTCULTUEAL SOCIETY. 



appears ; or, better still, to anticipate the presence of such diseases as are 

 known to attack particular kinds of plants under cultivation. This is not 

 always done. Drooping or obviously unhealthy plants are not removed 

 as promptly as they should be, and spraying to prevent the spread of a 

 disease is not sufficiently resorted to. 



I have said that cultivated plants well grown are not more susceptible 

 to disease than wild plants are, but when not w^ell grown such plants are 

 rendered liable to attack, and consequently suffer when healthy plants 

 would be able to resist successfully any attack made by the same fungus. 

 " Soft " foliage invites disease, and should always be guarded against as 

 much as possible ; unhealthy root-action, resulting from either too much 

 or too little water, too strong solutions of manure, or absence of oxygen 

 in the soil, also places the leaves at the mercy of numerous destructive 

 fungi that can only enter the tissues of the leaf when the general health 

 of the plant is below par. A proper amount of ventilation is indis- 

 pensable, and too much moisture in the atmosphere should be guarded 

 against, as it is very important to remember that fungus spores can 

 only germinate on the surface of a leaf and enter its tissues when the 

 surface of the leaf is damp. No fungus spore can germinate on a dry 

 surface ; therefore, when danger from a fungus epidemic is threatening, 

 it is well to keep the atmosphere as dry as conditions will allow. 



As usual, I am quite well aware it will be argued that plants must be 

 watered, and that houses must be damped down, &c. Exactly so, but use 

 moderation. Perhaps it is no exaggeration to say that in many instances 

 about twice as much water is used as is necessary. 



I exclude, as being outside the subject of my remarks, those cases 

 where plants are grown at high pressure and with only one object in view 

 — a crop. This is pure speculation, a kind of horticultural gambling, 

 where all laws and rules are set aside. Sometimes the experiment is 

 satisfactory, often not so, as would be expected under such artificial 

 conditions. 



Finally, it must be remembered that successful plant cultivation 

 depends to a large extent on the presence of various kinds of bacteria in 

 the soil. It is well known that excessive application of artificial manures 

 of various kinds destroys these indispensable organisms, and although an 

 ephemeral improvement may be observed in the condition of plants so 

 treated, due to the direct action of the manure, the after results are 

 worse than before its application, owing to the disappearance of the 

 bacteria. 



II.— Some Reasons why Peactical Men are not Successful in 



Teeating Plant Diseases. 



From amongst the many reasons that could be enumerated as 

 accounting for lack of success in combating fungus foes, the following 

 are of primary importance, and at the risk of being somewhat tedious 

 must be treated in detail. 



(1) The apparent mystery, and absence of anything obvious to account 

 for the presence of certain diseases said to be of fungus origin, is due, as 



